Polyethylene is used in the electrical and telecommunications business as an insulator for electrical wire and cable due to its very low electrical conductivity. For example, foamed low density polyethylene (LDPE), alone or blended with another polymer, is routinely used to insulate communication cable, such as coaxial cable and/or radio frequency cable. Polyethylene is especially suitable for high voltage cables due to its low dissipation factor at high voltage and its excellent mechanical properties.
Rapid advancements in the telecommunication industry are placing greater demand for higher signal quality in communication cable. One way to obtain higher signal quality in communication cable is to lower signal attenuation. Low levels (e.g., 1-10 moles parts per million (ppm)) of polar impurities in the polyethylene increases the electrical conductivity thus making it less suitable for high voltage, e.g., about 65 kV, electrical applications. These polar impurities typically originate from polar chain transfer agents that are used to control the polymer molecular weight and/or are the decomposition products of the peroxides that are used to initiate the polymerization.
LDPE is typically produced by polymerizing ethylene in a high pressure reactor using a peroxide initiator. Different peroxide initiators operate at different reactor temperatures depending on their half-life decomposition temperature. Initiators with lower half-life decomposition temperatures are used for lower reactor temperatures which can be advantageous to make higher density LDPE. Decomposition of peroxides is a highly exothermic event which makes the storage and transport of these peroxides very difficult, most notably for initiators with low half-life decomposition temperatures.
Thus, the art recognizes the need for polyethylene with low amounts of impurities, polar groups and unsaturation in order to achieve lower signal attenuation and lower dissipation factors in cable insulation. The art further recognizes the need for a LDPE electrical insulation material with a low dissipation factor that does not compromise the physical properties and/or processability properties of the LDPE. The art also recognizes the need for a class of initiators that decompose at the same temperature as commercial peroxides but decompose either endothermically or with much less heat release than standard peroxides. The lower amount of heat evolved from such a decomposition makes the initiator much more inherently stable and increases the self-accelerating decomposition temperature as compared to standard peroxides.